The infeed throat of a granulator hopper requires some type of barrier or door that will both permit entry of material and minimize the escape of noise and granulated product (flyback). This has been accomplished in the past through the use of metal pivoting doors as well as curtains made from a rubber compound. The latter are referred to as "aprons" and are commonly used on most granulators. A typical granulator requires a series of aprons, one behind the other, to effectively control the noise and flyback. These aprons have usually been fastened to the ceiling of the hopper, using several rivets or bolts. Regardless of whether rivets or bolts are used, the ability to remove the aprons for cleaning or for replacement is a long, tedious process.
Most manufacturers of granulators have used bolts because they are easier to remove than rivets. However, the presence of any fastener inside the granulator risks the possibility of a metal object accidentally falling into the knife area of the machine, causing damage to the knives. Also, it is inconvenient and time-consuming to reach deep into the throat of a hopper to remove and replace fasteners that retain the rear aprons.
A rod and tube method of attaching aprons has been used so that individual aprons may be removed for easy access. However, this is fairly expensive and still requires the removal and replacement of a multitude of fasteners.
The present invention comprises an apron rack assembly for a granulator that does not require any fasteners inside the infeed opening of the hopper. Broadly, the assembly consists of a rack which supports the aprons. The aprons have a long notch cut into each edge, so that once they are mounted onto the rack they are retained. Each apron drapes over a portion of the rack, such that is produces a double barrier and therefore replaces two conventional aprons. Usually, four or more barriers are required to be effective. The entire rack/apron assembly is then installed into the hopper opening. The rear of the rack rests on two small ledges inside the hopper and is secured in front by two bolts which are inserted along a horizontal axis through the upper lip of the hopper opening. As these bolts are installed, a portion of each apron is compressed or clamped between the top of the rack and the roof of the hopper, thus creating an added retention feature for the aprons. Both bolts are installed or removed from the outside of the hopper, making it unnecessary to have any fasteners inside the granulator.
To remove the rack with aprons for cleaning, the two bolts are simply removed, the front of the rack is lowered slightly, and the entire assembly is pulled out of the hopper. To remove and replace the aprons, the old ones are slipped or cut off and the new ones are slipped in. Once the rack is re-inserted into the hopper and the two bolts are installed, the job is complete. What used to take up to an hour can now be done in 5-10 minutes. Fewer individual aprons are required and each one is larger (one new apron replaces two of the old style).